System and method incorporating ultraviolet spectral fluorescence technology in sensor applications

ABSTRACT

Exemplary embodiments of a sensor arrangement may combine various technologies into an integrated sensor system operative to detect and to identify hazardous biological aerosols. An aerosol sampler may collect and concentrate particles acquired from the ambient environment, eliminating or minimizing particles that are potentially not relevant to the ensuing analysis. An integrated electro-optical subsystem or other detection technology may enable fast, accurate measurements of fluorescence characteristics associated with the acquired sample material, and may additionally identify biological agents present in the sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. provisionalapplication Ser. No. 60/493,942, filed Aug. 7, 2003, entitled “UVSFBIOSENSOR,” the disclosure of which is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Aspects of the present invention relate generally to the field of sensorapparatus, and more particularly to a system and method incorporatingultraviolet spectral fluorescence (UVSF) technologies in sensorapplications.

BACKGROUND

In conventional applications, point detection systems for detectingaerosol biological pathogens collect air samples and test the samplesfor the presence of undesirable airborne materials. One simple methodfor detecting the possible presence of biological pathogens is to detectthe ambient particle size distribution; in that regard, sudden variationof particle size distribution may be interpreted as indicative of thepresence of a biological agent. Anthrax, for example, ranges from about1 to about 5 microns (μm) in size, whereas environmental backgroundmaterials will span over a wider range of sizes. Laser scattering-basedtechniques are often employed in such detection systems, however, thistype of sensor technology cannot identify the nature of specificparticles (e.g., ascertain whether the particles are biological ornon-biological); accordingly, these systems are often used merely to cueor otherwise to trigger a second technique or an independent apparatusto begin analysis on the suspect material.

In order to detect the presence of biological material, itscharacteristic optical fluorescence may be exploited, since biologicalmaterial contains proteins that generally exhibit strong fluorescencewhen excited by ultraviolet (UV) light having certain wavelengths.Tryptophan, for example, which has a fluorescence peak at 340 nm whenexcited with UV light in the range of approximately 280 nm, is oftenused to determination the presence of biological material sincenon-biological material does not exhibit this peak. Some conventionalsystems employ a laser, a lamp, or some other UV source, to exciteairborne aerosols directly. One traditional sensor technology employs asingle-line UV laser and photomultiplier tube (PMT) detection system tointerrogate the fluorescence of the particles. Systems employing UVlasers are costly, require a moderate power supply source, and arecomplex at least to the extent that they attempt to measure eachindividual particle in the sample. Even more complex systems (e.g.,based on mass spectrometry) are also used for detection of biologicalmaterials.

In some traditional systems, particle impactors, virtual impactors, andcyclone samplers are used to separate airborne particles by size. Afterseparation, particle collection in water is very common so thatimmunoassay techniques that utilize-specific antigen-antibody bindingsor nucleic acid amplification by the polymerase chain reaction (PCR) canbe used to identify pathogens present in the sample. Again, thesesystems are exceedingly complex, and are deficient at least in thefollowing respects. Immunoassay techniques often take the form ofdisposable kits (similar to pregnancy tests, for example) and typicallyinvolve analysis of a color change after the sample is reconstitutedwith liquid on a test strip or other substrate. Other types of sensorsystems introduce a reagent tag to the sample, allow the tag to attachto the pathogen, then pass the sample over a sensor that detects theantibody tag rather than the pathogen itself. The nucleic acidamplification technologies require the use of a thermal cycle system toproduce copies of the gene material of the biological material. Theforegoing agent detectors require strictly controlled environmentalconditions (e.g., constant temperature) and many require consumablereagents for their operation. Hence, the traditional systems have veryhigh maintenance requirements and require use of expensive disposables.

What is needed is a system and method incorporating particlesize-selection, concentration, and ultraviolet spectral fluorescence(UVSF) technologies in sensor applications that require no reagents towork and include a sample collection strategy that allows archiving ofsample material for later analysis.

SUMMARY

Aspects of the present invention overcome the foregoing and othershortcomings of conventional technology, providing a system and methodincorporating ultraviolet spectral fluorescence (UVSF) technologies insensor applications.

In accordance with one exemplary embodiment, a method of detectingparticulate matter in an aerosol sample may comprise: collecting asize-selected sample of airborne particulate material; exposing thesample to electromagnetic excitation radiation having a plurality ofselected wavelengths; and detecting electromagnetic emission radiationemitted from the sample in response to the excitation radiation. Thecollecting may comprise depositing airborne particulate material on amedium, such as a filter medium, for example, and may additionallycomprise concentrating the particulate material.

As set forth in more detail below, the concentrating generally comprisesremoving particles larger than a first threshold size; in someapplications, the first threshold size is about ten microns.Additionally or alternatively, the concentrating may comprise removingparticles smaller than a second threshold size; in one disclosedembodiment, the second threshold size is about one micron. Specifically,the concentrating may comprise removing particles larger than a firstthreshold size and smaller than a second threshold size.

In accordance with some methods, the exposing comprises exposing thesample sequentially to each of the plurality of selected wavelengths;alternatively, the sample may be exposed simultaneously to each of theplurality of selected wavelengths. The excitation radiation isultraviolet (to short wavelength visible) radiation in some exemplaryembodiments. The detecting may comprise detecting radiation at each of aplurality of emission wavelengths, either simultaneously orsequentially. Some disclosed methods further comprise analyzing emissionradiation responsive to the detecting.

In accordance with another exemplary embodiment, a system for detectingparticulate matter in an aerosol sample generally comprises: means forcollecting a size-selected sample of airborne particulate material;means for exposing the sample to electromagnetic excitation radiationhaving a plurality of selected wavelengths; and means for detectingelectromagnetic emission radiation emitted from the sample in responseto the excitation radiation.

In some implementations, the means for collecting comprises means fordepositing airborne particulate material on a medium such as a filtermedium, for example. The means for collecting may additionally comprisemeans for concentrating the airborne particulate material, such as meansfor removing particles larger than a first threshold size, means forremoving particles smaller than a second threshold size, or both. Asdescribed above with reference to the foregoing method, the firstthreshold size is about ten microns and the second threshold size isabout one micron in some applications. The means for concentrating maycomprise a virtual impactor.

The means for exposing may comprise a lamp and an ultraviolet opticalfilter, for example, or an ultraviolet laser diode. In some versatilearrangements, the means for exposing comprises a lamp and a plurality ofultraviolet filters, and may further comprise means for sequentiallypositioning each of the plurality of ultraviolet filters between thelamp and the sample. In that regard, the means for sequentiallypositioning may comprise an ultraviolet filter wheel and means forrotating the filter wheel.

In some systems the means for detecting comprises a detector operativeto detect ultraviolet radiation at a selected emission wavelength. Thedetector may be embodied in or comprise a photomultiplier tube. In someimplementations, the means for detecting comprises a plurality ofdetectors, each of the plurality of detectors operative to detectultraviolet radiation at a selected one of a plurality of emissionwavelengths. As noted above, each of the plurality of detectors maycomprise a photomultiplier tube. Some systems may further comprise meansfor analyzing the detected emission radiation.

In one exemplary embodiment, the disclosed means for exposing comprisesmeans for exposing the sample sequentially to each of the plurality ofselected wavelengths; alternatively, the sample may be simultaneouslyexposed to each of the plurality of selected wavelengths. In somesystems, the means for exposing comprises means for exposing the samplesequentially to each of the plurality of selected wavelengths, and oneof the plurality of selected wavelengths is selected to identify aspecific interferent particle; accordingly, minimization of false alarmsmay be achieved. As set forth in more detail below, operation of themeans for concentrating the airborne particulate material may result inincreased sensitivity of the means for detecting.

In accordance with another embodiment, a sensor system may comprise: asize-separation component operative to collect a sample of airborneparticulate material and to deposit selected particulate matter from thesample having a size within a predetermined range on a medium; a sensorcomponent operative to expose the selected particulate matter toelectromagnetic excitation radiation having a plurality of selectedwavelengths and to detect electromagnetic emission radiation emittedfrom the selected particulate matter in response to the excitationradiation; and an analyzer component operative to execute an analysis ofthe selected particulate matter using data representative of theemission radiation acquired by the sensor component.

As set forth by way of example below, one embodiment of thesize-separation component deposits the selected particulate matter on afilter medium. In some systems, the size-separation component may beembodied in or comprise a virtual impactor. The sensor component maygenerally comprise an ultraviolet spectral fluorescence detector.

The foregoing and other aspects of the disclosed embodiments will bemore fully understood through examination of the following detaileddescription thereof in conjunction with the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified functional block diagram illustrating oneembodiment of a sensor system employing both size-specific aerosolsampling and sensitive ultraviolet spectral fluorescence detection anddiscrimination.

FIG. 2 is a simplified functional block diagram illustrating an airflowpattern through one embodiment of a sensor system.

FIG. 3 is a diagram illustrating various embodiments of high spectralresolution excitation and emission matrix plots of spectral fluorescentemission intensity expressed as a function of excitation wavelength.

FIG. 4 is a simplified graphical representation of data measurementsplotted against two spectral fluorescent indices optimized todiscriminate between bacterial spores, common interferents, and paperdust.

FIG. 5 is a simplified diagram illustrating another embodiment of asensor system employing both size-specific aerosol sampling andsensitive ultraviolet spectral fluorescence detection anddiscrimination.

FIG. 6 is a simplified flow diagram illustrating the general operationof one embodiment of a method of detecting particulate matter in anaerosol sample.

DETAILED DESCRIPTION

As set forth in more detail below, exemplary embodiments of a sensorarrangement may combine various technologies (such as ultravioletspectral fluorescence (UVSF) detection and size-specific aerosol sortingmethodologies, for example) into an integrated sensor system operativeto detect and to identify hazardous biological aerosols. In that regard,an aerosol sampler or similar component may collect and concentrateparticles acquired from the ambient environment. This process may beoperative to eliminate or to minimize particles that are potentially notrelevant to the ensuing analysis, and may additionally prepare acquiredsamples for spectral processing. An integrated electro-optical subsystemor other detection technology may enable fast, accurate measurements offluorescence characteristics associated with the acquired samplematerial, and may additionally identify biological agents present in thesample.

Turning now to the drawing figures, FIG. 1 is a simplified functionalblock diagram illustrating one embodiment of a sensor system employingboth size-specific aerosol sampling and sensitive ultraviolet spectralfluorescence detection and discrimination. The exemplary UVSF sensorembodiment of FIG. 1 may generally be characterized by integration oftwo technologies configured and operative to satisfy desired systemperformance requirements related to, but not limited to, operationalparameters such as sensitivity; false alarm rate; weight; measurementupdate interval specifications; and the like. In that regard, sensorsystem 100 may generally comprise an aerosol sampler component 110 andan optical/fluorescence detector component 120.

It will be appreciated that all or some (in various combinations) of thecomponents described in detail below with specific reference to FIGS. 1and 2 may be secured or otherwise disposed, either entirely orpartially, within a housing, case, or similar structure (not shown). Insome embodiments, for example, a hand-held or other portableimplementation of system 100 incorporating some or all of theillustrated elements may additionally comprise a housing, a rigid orsemi-rigid frame, one or more handles, castors or wheels, or otherstructural assemblies as generally known in the art of portable sensorsor other types of instrumentation.

Aerosol sampler component 110 may be operative to collect a sample ofairborne or atmospheric particulate material, along with gases in whichsuch particulate material may be suspended. In the illustratedembodiment, aerosol sampler component 110 may implement particle sizeseparation technology substantially to reduce the number of particles orthe volume of particulate matter in the sample to be analyzed. In thatregard, various size separation techniques or components may be employedselectively to remove, eliminate, minimize, or otherwise separate andfilter particles in accordance with the nature and size of theparticulate matter sought to be identified, overall system requirements,desired throughput characteristics, operational or functional aspects ofone or more system components, or other predetermined or preselectedparameters.

In one exemplary embodiment, particles in the sample having a nominalsize (e.g., as measured in accordance with diameter or other spatialdimension) or weight that falls outside of a specific or predeterminedrange may be filtered or removed by aerosol sampler component 110. Asindicated in FIG. 1, a low pass filter 111 may allow particulate matterhaving a nominal size below a first threshold value to pass, whileremoving or otherwise filtering particulate matter having a nominal sizeabove that first threshold value (e.g., >X μm in FIG. 1). Similarly, ahigh pass filter 112 may allow particulate matter having a nominal sizeabove a second threshold value to pass, while removing or otherwisefiltering particulate matter having a nominal size below that secondthreshold value (e.g., <Y μm in FIG. 1). During operation of theexemplary aerosol sampler component 110, particulate matter having asize characteristic greater than X may be removed or filtered from thesample material collected from the ambient air or atmosphere; similarly,particulate matter in the sample that has a size characteristic lessthan Y may be removed or filtered. This size separation operation isindicated schematically at functional block 119 in FIG. 1.

It will be appreciated that the first and second threshold values (X andY, respectively, in FIG. 1) may be arbitrary or otherwise susceptible ofnumerous variations. In that regard, the first and second thresholdvalues may vary in accordance with, among other things: the desiredfunctionality or operational characteristics of system 100; the natureand physical characteristics of the particulate sought to be identified;sensitivity and other parameters associated with optical/fluorescencedetector component 120; and the capabilities of the filter media orother technology employed in, or otherwise used in conjunction with, oneor both of filters 111,112. In some embodiments, the foregoing thresholdvalues may be selected in accordance with an expected or known sizerange representative or characteristic of a specific airborne or aerosolchemical, pollutant, or contaminant, for example, such as a biologicalweapons agent (BWA), noxious gas, bacterium, virus, toxin, or otherdeleterious particulate having a known or generally predictable size ordimensional characteristic. Specifically, first and second thresholdvalues of X=10 μm and Y=0.5 μm, respectively, may have particularutility in some applications.

As generally known in the art, a virtual impactor is a device operativeto concentrate airborne or otherwise suspended particles, and to sortthose particles without impacting them on a surface. In that regard, avirtual impactor generally uses aerodynamic inertial effects to separateairborne particles above a selected or predetermined diameter (or “cutsize”) from the rest of the particles in an aerosol cloud or atmosphericsample. The inlet flow of a typical virtual impactor may be split into amajor flow (containing a majority of the inlet air as well as a majorityof the particles smaller than the cut size) and a minor flow(representing a small fraction of the inlet air, but containing the vastmajority of the particles that are greater than the cut size). By way ofexample, if the cut size were 1 μm, the minor flow may contain particleshaving a size greater than 1 μm in concentrations up to ten times higherthan the inlet air; this concentration may vary as a function of theoperational characteristics or design parameters of the virtualimpactor.

Specifically, a virtual impactor component is a powerful processing toolthat may facilitate size-based sorting of particles and create highlyconcentrated aerosol clouds. In some embodiments of system 100, suchconcentration may improve the sensitivity of the analysis operation. Inaddition, concentrating particulate matter in a specific orpredetermined size range allows removal or minimization of particlesthat are not of interest from the aerosol cloud or atmospheric sample.Accordingly, one or both of filters 111,112 may be embodied in orcomprise a virtual impactor component, or otherwise utilize virtualimpactor technology.

Those of skill in the art will appreciate that background spectralsignals (i.e., noise or clutter) may be eliminated or substantiallyreduced by size selection operations sensitive to the 1-10 micron (μm)particle size range, or the 0.5-10 μm range, for many applications. Asset forth in more detail below, system 100 may concentrate the collectedsample material onto a filter medium, for example, or some othersuitable substrate or particle collector at a sample deposition area(generally depicted at reference numeral 170 in FIG. 1) for analysis byoptical/fluorescence detector component 120, and may additionallyarchive samples for further analysis.

In some implementations, and as illustrated in FIG. 1,optical/fluorescence detector component 120 may be embodied in orotherwise incorporate an ultraviolet spectral fluorescence (UVSF) sensor121 and a spectral analyzer 122. As indicated by the double-headed arrowin FIG. 1, UVSF sensor 121 may provide excitation illumination to samplematerial maintained or supported at sample deposition area 170, andreceive emission illumination from the sample. In some exemplaryembodiments, the illustrated optical/fluorescence detector component 120may generally be highly sensitive to biological materials and othersmall molecules and, additionally, may effectively discriminatedifferent types of materials in accordance with desired or predeterminedselection of UV-excitation and emission spectral bands.

Spectral analyzer 122 may facilitate the foregoing sensitivity anddiscrimination. Emission illumination data (representative of parameterssuch as, for example, wavelength and intensity of emitted radiation)received by UVSF sensor 121 may be provided to spectral analyzer 122 forsubsequent data processing and analysis. Numerous spectral analyses anddata processing methodologies are generally known in the art, and may besusceptible of alteration or variation in accordance with operationalcharacteristics or desired functionality of system 100. Accordingly,spectral analyzer 122 may include one or more data processing components(such as a microprocessor or microcomputer, for example) and attendantcomputer readable or electronic data recording media; additionally oralternatively, spectral analyzer 122 may comprise one or more interfacesallowing uni- or bi-directional data communication; accordingly, rawdata or data processed in whole or in part by spectral analyzer 122 maybe transmitted to a remote apparatus for further analysis, display,archival, and the like. Similarly, spectral analyzer 122 may include orcomprise one or more interfaces allowing bi-directional datacommunication with control electronics governing or otherwiseinfluencing operation of system 100 as set forth in more detail belowwith specific reference to FIG. 5. It will be appreciated that UVSFsensor 121 and spectral analyzer 122, though represented as individualfunctional blocks in FIG. 1, may be incorporated into a single componentor apparatus.

FIG. 2 is a simplified functional block diagram illustrating an airflowpattern through one embodiment of a sensor system. As set forth in moredetail below, the FIG. 2 embodiment may incorporate some or all of thephysical components and functional characteristics of system 100described above with specific reference to FIG. 1, including, but notlimited to, aerosol sampler component 210 and one or moreoptical/fluorescence detector components.

In accordance with the FIG. 2 embodiment, aerosol sampler component 210may generally comprise, inter alia, pre-filter (reference numeral 211)and micro-filter (reference numeral 212) components. In oneimplementation, pre-filter 211 may comprise or incorporate a SCALPER 33(TM) pre-filter apparatus (such as may be available throughMesoSystems). The SCALPER 33 (TM) is a virtual impactor device that maybe used to remove aerosol particles having a size (e.g., particlediameter) larger than 10 μm, for example, substantially as set forthabove with reference to FIG. 1. Alternatively, pre-filter 211 may employor incorporate an elutriation tube or knockout jar, as generally knownin the art; additional alterations or modifications may be implementedas necessary in accordance with overall system requirements.Irrespective of the specific device or combination of componentsemployed, pre-filter 211 may generally draw air from the environment(e.g., at inlet 251) at a specified or predetermined rate (e.g.,approximately 33 liters per minute (lpm)); in the illustratedembodiment, pre-filter 211 may be operative to execute the operationdepicted at functional block 111, i.e., to remove or otherwise to filterparticles having a nominal size greater than a first threshold value(e.g., such as 10 μm) as set forth in detail above. The minor flow(generally represented by reference numeral 258 in FIG. 2) throughpre-filter 211 may have a high concentration of particles above the cutsize, X; this minor flow may be exhausted or otherwise disregarded,removing such particles from the airflow, and subsequent analysis, ofsystem 100.

The major flow (generally represented by reference numeral 259 in FIG.2) through pre-filter 211 may be directed to micro-filter 212. It willbe appreciated that one or more components, such as coupling adapter245, may be selectively employed to couple pre-filter 211 andmicro-filter 212. The specific structural arrangement andinterconnection between components may vary in accordance with thephysical characteristics (e.g., conduit dimensions) or functionalparameters (e.g., operational flow rates) associated with pre-filter211, micro-filter 212, or both. In particular, coupling adapter 245 maybe configured and operative to communicate major flow 259 output frompre-filter 211 to an inlet 241 of micro-filter 212. As noted above,major flow 259 may have a high concentration of particles smaller thanX=10 82 m or some other threshold value.

In the FIG. 2 embodiment, micro-filter 212 may be embodied in orotherwise comprise a MICROVIC (TM) filter (such as may be availablethrough MesoSystems). The MICROVIC (TM) model MVA-33A, for example, maybe suitable in many applications of micro-filter 212. By way of example,this device may have a 33 lpm inlet flow rate (e.g., at inlet 241) and a3 lpm minor flow rate (minor flow is generally indicated at referencenumeral 248), with a cut size of approximately Y=1.0 μm and an averageconcentration factor of 8 over the 1-5 micron range. Major flow(generally indicated at reference numeral 249) through micro-filter 212may carry a high percentage of particles having a size dimension belowthe cut size, Y, as set forth above. Particles of a specified range maythen be delivered to filter media 270, or some other specified sampledeposition area. The major flow (generally represented by referencenumeral 249 in FIG. 2) through micro-filter 212 may have a highconcentration of particles below the cut size, Y; this major flow may beexhausted or otherwise disregarded, removing such particles from theairflow, and subsequent analysis, of system 100.

In accordance with the foregoing, a sample deposition area (generallyrepresented as filter media 270) may be optimized for one or moredifferent types of UVSF detector such as represented by referencenumeral 121 in FIG. 1, for example. In the event that a higher sampleflow rate is necessary or desired, for instance, to achieve a requireddetection limit or false alarm rate, a two-stage MICROVIC (TM) system orother suitable device may be implemented at micro-filter 212 to samplelarger volumes of air or sample material.

In some implementations, such a two-stage system may provide a particleconcentration factor (or ratio) of approximately 100:1 or higher, with asample flow rate of approximately 400 lpm. It will be appreciated thatthe engineering trade for such extra sampling capacity may result inincreased power consumption, cost, size of system 100, or somecombination thereof. On the other hand, substantial contributions tooverall sensor performance may be attributed to the ability of aerosolsampler component 210 to provide size selection, for example, on theorder of the 1.0-10 μm particle size range. Consequently, particles of aselected size range may be presented for spectral sensor analysis. Whereselectively implemented, the foregoing (or an equivalent) size-selectiveapproach may substantially reduce the amount of background spectralclutter attributable to ambient interferants (e.g., such as pollen)having size characteristics that lie outside those of a selected target(or “threat”) particle size range.

As noted above, some embodiments of system 100 such as described abovewith reference to FIGS. 1 and 2 may have particular utility in detectingand identifying airborne biological agents or molecules present in acollected atmospheric sample. In that regard, it is noted that theintrinsic fluorescence emission of biological materials may becharacterized as having broad, smooth, spectral features that can span aspectral range as wide as 250 nm. A general understanding of thecomposition of biological aerosols may be beneficial in discriminatingbiological warfare agents from naturally occurring materials. Typically,the fluorescence characteristics of biological materials may beattributable to one or more of the following sources: the aromatic aminoacids tryptophan, tyrosine, and phenylalanine; nicotinamide adeninedinucleotide compounds (NAD(P)H); flavins; and chlorophylls.

Of the foregoing, both tryptophan and NAD(P)H emissions are prevalent inpathogens and may be exploited for identification of same. Tryptophan,for example, excites well with excitation illumination havingwavelengths in the 250-290 nm range, and generally fluoresces in the325-400 nm range. Similarly, NAD(P)H has an excitation/emission peak(EEP) of fluorescence in the respective ranges of about 320-370nm/425-480 nm. Non-biological materials generally do not exhibit thesesame EEPs; accordingly, a UVSF subsystem, such as optical/fluorescencedetector component 120, for instance, may provide very sensitivealarming capabilities for biological materials. Even though manybiological materials have similar chemical structures orcharacteristics, each respective fluorescence “fingerprint” will vary,enabling optical/fluorescence detector component 120 not only to detectthe presence of biological materials, but also to discriminate amongthem. In addition, specific excitation and/or emission wavelengths maybe selected to minimize or to eliminate the effects of commoninterferents and to reduce false alarms.

FIG. 3 is a diagram illustrating various embodiments of high spectralresolution excitation and emission matrix plots of spectral fluorescentemission intensity expressed as a function of excitation wavelength. Asindicated in FIG. 3, a fluorescence “fingerprint” for a particularmolecule may be visualized graphically by a fluorescenceexcitation/emission matrix (EEM) plot. In the exemplary graphs depictedin FIG. 3, high spectral resolution EEM plots illustrate spectralfluorescent intensity as a function of excitation wavelength. The darkshaded areas in the lower left of each plot generally indicate highfluorescence responses, while the shaded areas to the right of each plotgenerally indicate low fluorescence responses. The EEMs for the bacteriaBacillus subtilis var. globigii (Bg) and Bacillus thuringiensis (Bt),the virus MS2, and the protein Ovalbumin are shown. The bacteria, virus,and toxin EEMs are clearly different, though the two bacteria EEMs arevery similar. In that regard, the strong peak in the 250-350 nm range isconsistent with the presence of tryptophan in the sample, and the peakin the visible region of the bacteria EEMs is consistent with thepresence of NAD(P)H.

It will be appreciated that an EEM “fingerprint” may be particularlyuseful for detecting and discriminating unknown materials; in someconventional technological implementations, however, such fingerprintingmay be difficult to obtain with a low-cost, lightweight, real-timesensor. In an alternative approach, one or more (or an entire suite of)discrete EEP combinations that characterize specific pathogens andrelevant or typical associated background or clutter materials may beidentified. Such identification may be effectuated or facilitated byevaluating high resolution EEMs of selected materials and combinationsof materials. The foregoing procedure represents a fundamental departurefrom traditional high-resolution analyses of an emission spectrumgenerated by a single excitation wavelength.

In accordance with some embodiments, for example, excitationillumination may be provided with up to four excitation wavelengths;highly sensitive photomultiplier tubes (PMTs) may be employed, forexample, in conjunction with wavelength selective optical filters, toallow simultaneous detection at four wavelengths. It will be appreciatedthat the multiple EEPs may identify different molecules within aspecific pathogen or sample, and that wide optical bandwidths achievedusing discrete optical filters may increase the signal-to-noise-ratio(SNR). Table 1 shows a sample of selected EEPs by way of example and notby way of limitation. Those of skill in the art will appreciate that,since optical filters and lamp apparatus may be selectively changed orreadily altered, the EEPs set forth in Table 1 may be modified inaccordance with desired system performance, the nature of the particlesor material sought to be identified, and so forth. TABLE 1 ExcitationWavelength (nm) Emission Wavelength (nm) 254 330 380 420 450 280 330 380420 450 320 380 420 450 365 420 450

FIG. 4 is a simplified graphical representation of data measurementsplotted against two spectral fluorescence indices optimized todiscriminate between bacterial spores, common interferents, and paperdust. The data represented in FIG. 4 were obtained from a sensor systemsuch as described above with specific reference to FIGS. 1 and 2 andemploying a UVSF sensor 121 and a spectral analyzer 122. Algorithmsproducing the FIG. 4 data combined measurements of three EEPs (280/340nm, 280/450 nm, and 365/450 nm, respectively) to produce the two indices(the abscissa and ordinate in FIG. 4). In addition, the system was usedto measure the threat simulants and some potential interferents relevantto this particular application; the results of these measurementsdocument the ability to discriminate between many of these agents. Asillustrated in FIG. 4, the various agents and interferents cluster atdifferent locations within the parameter space.

In some embodiments, a suitable UVSF detection algorithm may analyze EEPmeasurements; as noted above, such EEP measurements may be verysensitive to biological materials. The EEMs depicted in FIG. 3, forexample, and the data represented in FIG. 4 show clear differences inresponse between bacteria, viruses, and toxins. These EEP measurementsmay be employed to define points in an n-dimensional sample space inwhich different materials may be expected to cluster in differentregions as illustrated in FIG. 4. Standard analysis techniques such as aneural net or principal component analysis, for example, may be employedto exploit this clustering and to detect and identify specificparticular material (such as BWAs, for instance) in the collectedsample.

In accordance with some embodiments, design of system 100 may be modularin nature and may support or accommodate testing in a wind tunnel, forexample, to facilitate calibration or validation studies. In addition tothe size selective aerosol sampling sub-system and the optical detectorsub-system described above, some implementations may additionallyinclude an automated control and user interface sub-system.

In that regard, FIG. 5 is a simplified diagram illustrating anotherembodiment of a sensor system employing both size-specific aerosolsampling and sensitive ultraviolet spectral fluorescence detection anddiscrimination. System 500 may generally comprise or incorporate all ofthe components and functionality set forth in detail above; further, theFIG. 5 embodiment additionally comprises an automated control and userinterface sub-system, generally represented by the electronic componentindicated as associated with the aerosol sampler component 110.

It will be appreciated that system 500 may additionally comprise a userinterface operably coupled with the illustrated electronics; such a userinterface may enable user input and provide real-time or near real-timedisplay of operational parameters, computation results, system status,and so forth. In some implementations, a suitable user interfaceappropriate for a portable version of system 500 may generally beembodied in or comprise, for example, a touch sensitive displayoperative both to receive input and dynamically to provide requested orautomated output. Additionally or alternatively, system 500 may alsocomprise one or more of the following, without limitation: a liquidcrystal display (LCD) panel or other display or monitor apparatus; lightemitting diode (LED) arrays or other output indicators; a keyboard orkey pad; a track ball, mouse, or other input component; and the like.Numerous and varied electronic input and output technologies aregenerally known in the art of allowing a user to interface with anelectronic or microprocessor-controlled apparatus.

Electronics may generally comprise a microprocessor, a microcomputer, aprogrammable logic controller (PLC), or other selectively programmableor reconfigurable electrical elements. Additionally, one or morerecordable and readable media (such as Read-Only Memory (ROM), RandomAccess Memory (RAM), hard or floppy disk media, optical ormagneto-optical disk media, or the like) may be implemented, allowingprogramming instruction sets and data to be selectively accessed asneeded by control electronics or the user interface component. Varioushardware, software, and firmware modules may be employed for theforegoing purposes as generally known in the art.

Electronics, either independently or in conjunction with data andinstruction sets encoded on computer readable media, may be employed,for example, to receive user input and to execute various controlfunctions for system 500. In that regard, electronics may control orotherwise influence flow rates through the pre-filter and themicro-filter, for example, or to prompt a user for input followingsample collection procedures.

As noted above, aerosol sampler component 110 may generally include aSCALPER 33 (TM) pre-filter coupled to a MICROVIC (TM) Model MVA33Avirtual impactor micro-filter. Pre-filtering operations may efficientlyremove large particles from the sample stream; as set forth above, suchpre-filtering may employ virtual impactor technology in some instances,or an elutriation tube or knockout jar. For many applications configuredfor biological sample analysis, pre-filtering may be optimized toprovide a cut size of approximately 10 μm, though other cut sizes may beappropriate for different pre-filter operations.

In the FIG. 5 implementation, the <10 μm particulates are passed to themicro-filter which, in turn, may be configured and operative to removesmall particulates from the sample air stream; additionally, themicro-filter may concentrate selected particulates (i.e., those within apredetermined size range) in the sample air flow path. In that regard,the micro-filter in FIG. 5, optimized for biological sample collectionand analysis, is generally designed to have a cut size of approximately0.5 μm; as noted above, other cut sizes are contemplated, and may bemore appropriate for different applications. In some situations,optimizing the micro-filter for other cut sizes may potentially resultin reduced throughput efficiency.

In the foregoing exemplary embodiments (such as that illustrated in FIG.2), major flows 259,249 of the SCALPER 33 (TM) and the MICTROVIC (TM),respectively require a relatively low pressure drop (˜10-inches of watercolumn), and are therefore operable in conjunction with small,light-weight, DC powered air movers. Only the last stage of sample flow(i.e., the 3 lpm minor flow 248 from the micro-filter 212 in FIG. 2)requires a modest pressure drop of ˜2 PSIG to accommodate the requiredair flow through filter media 270. In most practical applications, sucha flow may be generated by a small, DC powered rotary vane pump orsimilar apparatus.

As illustrated in FIGS. 1 and 5, optical/fluorescence detector component120 may generally comprise the following components: a mercury-xenon (orsimilar) lamp coupled (or otherwise operative in conjunction) with anoptical filter wheel, enabling generation of excitation light at arequired or selectively adjustable wavelength or range of wavelengths; asolid-state optical wave guide operative to deliver such excitationlight to the sample; and an array of PMTs (each of which may be equippedwith a narrow band pass emission optical filter) to quantifyfluorescence emissions from the collected sample for a specificwavelength range. It will be appreciated that generation of excitationlight at a selected wavelength or range of wavelengths as describedabove may be accomplished with, or in conjunction with, any of varioustypes of light generating apparatus or equipment known in the art ordeveloped and operative in accordance with known principles; forexample, UV laser diodes or other light sources may selectively provideexcitation light in accordance with system requirements and may beemployed in addition to, or as an alternative to, a lamp and filterwheel arrangement. The present disclosure is not intended to be limitedto any particular visible light (or other electromagnetic excitationradiation) generating technology.

System 500 may exhibit excellent signal-to-noise-ratio (SNR)characteristics, in part, because the PMTs may be closely coupled,eliminating or minimizing the need for lenses. In addition, theconfiguration depicted in FIG. 5 may allow simultaneous measurement offour (or more) emission wavelengths. Those of skill in the art offluorescence detection will appreciate that filtered lamps may havesignificant advantages over UV lasers for many applications; some suchadvantages include greater variations in excitation wavelengths, asmaller footprint, increased reliability, and lower cost. As notedabove, however, UV laser diodes or other excitation radiation sourcesmay be employed as appropriate in some implementations.

An embedded single board computer (SBC) may be implemented as describedabove with specific reference to the electronics component illustratedin FIG. 5. In that regard, the SBC may provide selected or requiredsystem control timing and ancillary data management; additionally oralternatively, an SBC may facilitate an interface between system 500 andoperators, telemetry systems, or both. Onboard data storage may beprovided by flash RAM or other recordable and computer readable media.It will be appreciated that such an SBC may also support a 10bT Ethernetcommunications link, for example, or other bi-directional datacommunication technology. Other examples of data communications hardwareand protocols include, but are not limited to, FireWire (TM), UniversalSerial Bus (USB), BlueTooth (TM), and asynchronous transfer protocol(ATP) technologies. Such communication capabilities may allow system 500to communicate with an external laptop computer, for instance, or otherremote computing or data processing apparatus. Accordingly, dataretrieval and performance monitoring (e.g., during static testing) maybe facilitated.

In operation, a sensor system such as set forth above may acquire samplematerial and analyze multiple samples in parallel. While a first sample(first material) is being analyzed, a second sample (second material) isaccumulating on appropriate filter media. When the second sample isready for analysis and the first analysis is complete, the filter mediaadvances to transfer the second sample to an appropriate position to beprocessed by the analyzer; simultaneously, a third sample startsaccumulating on a new location on the filter media. It will beappreciated from the foregoing that sample material may be stored orotherwise archived on the filter media or other substrate for subsequentanalysis; such analysis may be performed, for example, by a sensorsystem such as illustrated in FIG. 1, or by an independent apparatus.The UV fluorescence analysis set forth herein may sequentially orsimultaneously excite each successive sample at a plurality of (e.g.,four) excitation wavelengths. For each excitation wavelength, thefluorescence is measure simultaneously at 2-4 emission wavelengths (suchas set forth in Table 1, for example). These measurements are recordedand analyzed to determine the presence of BWAs or other material soughtto be identified.

FIG. 6 is a simplified flow diagram illustrating the general operationof one embodiment of a method of detecting particulate matter in anaerosol sample. The operations depicted in FIG. 6 may be executed orfacilitated by a system such as that set forth in detail above.

As indicated at block 601, a method of detecting particulate matter inan aerosol sample may begin by collecting a sample or sample material(e.g., from the atmosphere) containing airborne or aerosol particulatesor other material to be studied. The particles within the airborneparticulate material larger than a first size or threshold value may beremoved as indicated at block 602. Similarly, the particles within theairborne particulate material smaller than a second size or thresholdvalue may be removed as indicated at block 603. The operations depictedat blocks 602 and 603 result in collection of size-selected sampleparticles.

As set forth in more detail above, the first size (i.e., thresholdvalue) may be approximately 10 μm, and the second size (i.e., thresholdvalue) may be approximately 1 μm or smaller (such as 0.5 μm) for manyapplications. Particles having a size within a predetermined range (asdefined by the threshold values, for example) may be provided to adeposition area as indicated at block 604. The operation at block 604,i.e., concentrating the airborne particles smaller than the firstthreshold size and larger than the second threshold size on a filtermedium or other substrate, for example, may be effectuated or influencedby the pre-filter and micro-filter components set forth above.

As indicated at block 605, particles from the sample material that arewithin the selected size range may be exposed to electromagneticexcitation radiation; as set forth above, such excitation radiation maybe within a predetermined or preselected range of wavelengths, whichgenerally may be application-specific. In many applications, UVradiation may have particular utility. In some embodiments, theexcitation depicted at block 605 may include providing excitationillumination or radiation at a plurality of wavelengths (such as two orfour), either simultaneously or sequentially.

As indicated at block 606, electromagnetic emission radiation emittedfrom the sample material in response to the excitation radiation may bedetected as set forth above. The operation depicted at block 606 mayinclude detecting emission radiation at each of a plurality ofwavelengths, either sequentially or simultaneously. Data representativeof the emission radiation may be acquired (block 607) for subsequenttransmission, storage, analysis, or some combination thereof.

Aspects of the present invention have been illustrated and described indetail with reference to particular embodiments by way of example only,and not by way of limitation. It will be appreciated that variousmodifications and alterations may be made to the exemplary embodimentswithout departing from the scope and contemplation of the presentdisclosure. It is intended, therefore, that the invention be consideredas limited only by the scope of the appended claims

1. A method of detecting particulate matter in an aerosol sample; saidmethod comprising: collecting a size-selected sample of airborneparticulate material; exposing the sample to electromagnetic excitationradiation having a plurality of selected wavelengths; and detectingelectromagnetic emission radiation emitted from the sample in responseto the excitation radiation.
 2. The method of claim 1 wherein saidcollecting comprises depositing airborne particulate material on amedium.
 3. The method of claim 2 wherein said medium comprises a filtermedium.
 4. The method of claim 1 wherein said collecting comprisesconcentrating the particulate material.
 5. The method of claim 4 whereinsaid concentrating comprises removing particles larger than a firstthreshold size.
 6. The method of claim 5 wherein said first thresholdsize is about ten microns.
 7. The method of claim 4 wherein saidconcentrating comprises removing particles smaller than a secondthreshold size.
 8. The method of claim 7 wherein said second thresholdsize is about one micron.
 9. The method of claim 4 wherein saidconcentrating comprises removing particles larger than a first thresholdsize and smaller than a second threshold size.
 10. The method of claim 9wherein said first threshold size is about ten microns and said secondthreshold size is about one micron.
 11. The method of claim 1 whereinsaid exposing comprises exposing the sample sequentially to each of theplurality of selected wavelengths.
 12. The method of claim 1 whereinsaid excitation radiation is ultraviolet radiation.
 13. The method ofclaim 1 wherein said detecting comprises detecting radiation at each ofa plurality of emission wavelengths.
 14. The method of claim 13 whereinsaid detecting comprises detecting radiation simultaneously at each ofthe plurality of emission wavelengths.
 15. The method of claim 1 furthercomprising analyzing emission radiation responsive to said detecting.16. A system for detecting particulate matter in an aerosol sample; saidsystem comprising: means for collecting a size-selected sample ofairborne particulate material; means for exposing the sample toelectromagnetic excitation radiation having a plurality of selectedwavelengths; and means for detecting electromagnetic emission radiationemitted from the sample in response to the excitation radiation.
 17. Thesystem of claim 16 wherein said means for collecting comprises means fordepositing airborne particulate material on a medium.
 18. The system ofclaim 17 wherein said medium comprises a filter medium.
 19. The systemof claim 16 wherein said means for collecting comprises means forconcentrating the airborne particulate material.
 20. The system of claim19 wherein the means for concentrating comprises means for removingparticles larger than a first threshold size.
 21. The system of claim 20wherein said first threshold size is about ten microns.
 22. The systemof claim 19 wherein said means for concentrating comprises means forremoving particles smaller than a second threshold size.
 23. The systemof claim 22 wherein said second threshold size is about one micron. 24.The system of claim 19 wherein said means for concentrating comprisesmeans for removing particles larger than a first threshold size andsmaller than a second threshold size.
 25. The system of claim 24 whereinsaid first threshold size is about ten microns and said second thresholdsize is about one micron.
 26. The system of claim 19 wherein said meansfor concentrating comprises a virtual impactor.
 27. The system of claim16 wherein said means for exposing comprises a lamp and an ultravioletfilter.
 28. The system of claim 16 wherein said means for exposingcomprises an ultraviolet laser diode.
 29. The system of claim 27 whereinsaid means for exposing comprises a lamp and a plurality of ultravioletfilters.
 30. The system of claim 29 further comprising means forsequentially positioning each of said plurality of ultraviolet filtersbetween said lamp and the sample.
 31. The system of claim 30 whereinsaid means for sequentially positioning comprises an ultraviolet filterwheel and means for rotating said filter wheel.
 32. The system of claim16 wherein said means for detecting comprises a detector operative todetect ultraviolet radiation at a selected emission wavelength.
 33. Thesystem of claim 32 wherein said detector comprises a photomultipliertube.
 34. The system of claim 16 wherein said means for detectingcomprises a plurality of detectors, each of said plurality of detectorsoperative to detect ultraviolet radiation at a selected one of aplurality of emission wavelengths.
 35. The system of claim 34 whereineach of said plurality of detectors comprises a photomultiplier tube.36. The system of claim 16 further comprising means for analyzing thedetected emission radiation.
 37. The system of claim 16 wherein saidmeans for exposing comprises means for exposing the sample sequentiallyto each of the plurality of selected wavelengths.
 38. The system ofclaim 16 wherein said means for exposing comprises means for exposingthe sample sequentially to each of the plurality of selected wavelengthsand wherein one of the plurality of selected wavelengths is selected toidentify a specific interferent particle.
 39. The system of claim 19wherein operation of said means for concentrating the airborneparticulate material results in increased sensitivity of said means fordetecting.
 40. A sensor system comprising: a size-separation componentoperative to collect a sample of airborne particulate material and todeposit selected particulate matter from the sample having a size withina predetermined range on a medium; a sensor component operative toexpose the selected particulate matter to electromagnetic excitationradiation having a plurality of selected wavelengths and to detectelectromagnetic emission radiation emitted from the selected particulatematter in response to the excitation radiation; and an analyzercomponent operative to execute an analysis of the selected particulatematter using data representative of the emission radiation acquired bysaid sensor component.
 41. The system of claim 40 wherein saidsize-separation component deposits the selected particulate matter on afilter medium.
 42. The system of claim 41 wherein said size-separationcomponent comprises a virtual impactor.
 43. The system of claim 40wherein said sensor component comprises an ultraviolet spectralfluorescence detector.